The present invention relates to a new and improved method and apparatus for measuring the velocity of moving objects or the like.
There is already known to the art both a method for space monitoring by means of pulsed directional radiation and also an apparatus for the performance of such method. Significant in this regard is International Patent Publication No. WO 80/02764, dated Dec. 11, 1980, and the cognate U.S. Pat. No. 4,319,332, granted Mar. 9, 1982. In such documents there is disclosed, among other things, a method which is manifested by the features that at least one virtual line or virtual surface is correlated to a roadway or the like, there is detected the crossing of a virtual line or the penetration of a virtual surface by at least one vehicle, and such event is evaluated and/or recorded.
There is further disclosed the manner in which, with the aid of measuring beams, there can be measured a moving object as concerns its movement, trajectory and/or velocity and/or acceleration. Additionally, in such documents there is disclosed a beam splitter system for the surface-like or spatial beam splitting or beam fanning.
With the aid of the objects of such prior art, both as concerns the method and apparatus aspects, it is obvious for accomplishing velocity measurements of moving objects to direct pulsed optical measuring beams from a lateral position towards the path of travel of such object, and such measuring beams, starting from at least one point, are directed in at least one direction towards such path of travel.
By measuring and evaluating the transit or travel times of optical pulses which have been reflected at the moving objects it is possible to measure coordinates of such objects at different points in time. From such coordinates or the distance vectors to the reflection locations, on the one hand, and the timewise course of the measurements, on the other hand, it is possible to compute velocity values and to correlate such to predetermined objects.
The measuring beams which are to be directed towards the path of travel of the object which is to be detected can emanate from a point and can be chosen to extend at a predetermined angle p with respect to one another. Also, the measuring beams emanating from a plurality of points, can be chosen to extend parallelly at defined spacings from one another. Preferably, the directions of the measuring beams are chosen such that they extend in a single plane which is disposed at least approximately parallel to the path of travel of the object to be detected.
What is disadvantageous with a method and apparatus of the previously described type is that, the measuring beams which are stationary in space are intersected, or cut, during the measurement, by the moving objects, whereby the objects to be measured are detected. For the timewise exact determination of the entry of a relatively rapidly moving object into a measuring beam it is necessary for the pulse frequency of such measuring beam to possess a sufficiently high value, so that the resultant quantization error in the determination of the entry time point is smaller by at least one order of magnitude than the time duration which is needed for moving through the path or distance between two successive measuring beams.
For the practical application of such equipment in public traffic, for instance for monitoring motor vehicle traffic, the permissible pulse frequency of the measuring beams which is to be employed, with a predetermined pulse output, is limited to a certain upper threshold value by virtue of the so-called eyesight or eye safety regulations. It has been found that the velocity measuring range of practical constructions of equipment for velocity measurements in accordance with the aforementioned method, are practically too markedly limited because of the required pulse frequency, on the one hand, owing to the quantitization errors which must be observed and, on the other hand, because of the eye safety regulations which must be complied with. Therefore, velocity measuring methods and equipment for the performance thereof working in accordance with the described principle, are too markedly limited or, in fact, unusable for certain fields of application.
Additionally, from German Patent Publication No. 2,723,584, published Nov. 30, 1978, there is known a prior art velocity measuring apparatus. The drawback discussed in conjunction with the first mentioned patent is avoided with this German Patent Publication in that, the object to be measured is continuously followed or tracked by a measuring beam and is simultaneously measured by means of such measuring beam. Here, as long as the angle between the direction of movement of an object which is to be detected and the measuring beam transmitted towards such object is sufficiently small, i.e. approximately below 10.degree., and, if the accuracy requirements for the velocity measurement are not extremely high, for instance must only be accurate to about 1.5%, then the aforementioned angle need not be taken into account. The velocity of the object then can be directly determined from the change of the distance to the object measured with each pulse and resulting during the optical tracking of the object. The point in time of entry of the object into the measuring beam, with this prior art method, is meaningless for the measurement accuracy, and there can be selected for the pulse frequency a value which has no detrimental consequences as concerns protecting the eyes of human beings.
But also this last-mentioned equipment does not operate faultlessly under all practical conditions. Among others, the following drawbacks are particularly worthy of mention:
1. It is presupposed or assumed when using such velocity measuring apparatus that the measuring beam always impinges at the same place or spot upon the object to be measured during the entire measurement operation. Since such type of velocity measuring apparatus, according to a preferred construction, constitutes a manually held piece of equipment, somewhat similar in its design to a photographic camera, it is impossible to avoid shifting of the impact point of the measuring beam at the object to be measured during the measuring operation. Above all, with an irregularly configured or contoured object, such as motor vehicles, such has the effect that a sequence of distance values to different impact points at an object to be measured undesirably constitutes the basis of the velocity determination. This, of course is associated with a considerable ambiguity in the reliability of the measurement result. In the aforementioned German Patent publication there is specifically mentioned the known Gauss' error squaring method as a possibility of obtaining a reliable final measurement result from a multiplicity of unreliable measurement results. However, the mentioned German Patent publication does not disclose a more exact method for determining the reliability of individual measurement results, nor does it disclose a technique for eliminating measurement results which arise during the shifting of the impact point of the measuring beam.
2. Particularly if there must be accomplished velocity measurements in the presence of dense or heavy traffic, in other words when, viewed from the standpoint of the measuring apparatus, a plurality of objects, here vehicles for instance, move within a relatively narrow angular range, it is impossible to preclude that the measuring beam, during a measurement operation will at least periodically impinge upon a number of objects having different velocities. Since, in such case, the formed distance values to the objects are to be considered as hybrid values, the thus derived velocity values likewise must be evaluated as hybrid values of the velocities of the individual vehicles. A velocity measuring apparatus where such hybrid value formation can occur in an uncontrolled fashion, based upon measurements to different objects, i.e. vehicles, is however practically unusable as a reliable means for monitoring traffic, because of the possibility of an alleged traffic violator to legally challenge the measurement results in court. In the aforementioned publication there has not been disclosed in any manner how the formation of such hybrid values can be detected and, if desired, suppressed or eliminated.